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<html>
<head>
<title>Vorbisfile - function - ov_open_callbacks</title>
<link rel=stylesheet href="style.css" type="text/css">
</head>
<body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff">
<table border=0 width=100%>
<tr>
<td><p class=tiny>Vorbisfile documentation</p></td>
<td align=right><p class=tiny>vorbisfile version 1.68 - 20030307</p></td>
</tr>
</table>
<h1>ov_open_callbacks</h1>
<p><i>declared in "vorbis/vorbisfile.h";</i></p>
<p>This is an alternative function used to open and initialize an OggVorbis_File
structure when using a data source other than a file. It allows you to specify custom file manipulation routines and sets up all the related decoding structure.
<p>Once this has been called, the same <tt>OggVorbis_File</tt>
struct should be passed to all the libvorbisfile functions.
<p>
It is often useful to call <tt>ov_open_callbacks()</tt>
simply to determine whether a given stream is a vorbis bitstream. If the
<tt>ov_open_callbacks()</tt>
call fails, then the data is not recognizable as such. When you use <tt>ov_open_callbacks()
</tt>for
this, you should close or otherwise deallocate your <tt>datasource</tt> if, and only if, the
<tt>ov_open_callbacks()</tt>
call fails. If it succeeds, you must call <a href=ov_clear.html>ov_clear()</a> to clear
the decoder's buffers and call your close callback.<p>
See also <a href="callbacks.html">Callbacks and Non-stdio I/O</a> for information on designing and specifying the required callback functions.<p>
<br><br>
<table border=0 color=black cellspacing=0 cellpadding=7>
<tr bgcolor=#cccccc>
<td>
<pre><b>
int ov_open_callbacks(void *datasource, <a href="OggVorbis_File.html">OggVorbis_File</a> *vf, char *initial, long ibytes, <a href="ov_callbacks.html">ov_callbacks</a> callbacks);
</b></pre>
</td>
</tr>
</table>
<h3>Parameters</h3>
<dl>
<dt><i>datasource</i></dt>
<dd>Pointer to a data structure allocated by the calling application, containing any state needed by the callbacks provided.</dd>
<dt><i>vf</i></dt>
<dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile
functions. Once this has been called, the same <tt>OggVorbis_File</tt>
struct should be passed to all the libvorbisfile functions.</dd>
<dt><i>initial</i></dt>
<dd>Typically set to NULL. This parameter is useful if some data has already been
read from the stream and the stream is not seekable. It is used in conjunction with <tt>ibytes</tt>. In this case, <tt>initial</tt>
should be a pointer to a buffer containing the data read.</dd>
<dt><i>ibytes</i></dt>
<dd>Typically set to 0. This parameter is useful if some data has already been
read from the stream and the stream is not seekable. In this case, <tt>ibytes</tt>
should contain the length (in bytes) of the buffer. Used together with <tt>initial</tt>.</dd>
<dt><i>callbacks</i></dt>
<dd>A completed <a href="ov_callbacks.html">ov_callbacks</a> struct which indicates desired custom file manipulation routines.</dd>
</dl>
<h3>Return Values</h3>
<blockquote>
<li>0 for success</li>
<li>less than zero for failure:</li>
<ul>
<li>OV_EREAD - A read from media returned an error.</li>
<li>OV_ENOTVORBIS - Bitstream is not Vorbis data.</li>
<li>OV_EVERSION - Vorbis version mismatch.</li>
<li>OV_EBADHEADER - Invalid Vorbis bitstream header.</li>
<li>OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.</li>
</ul>
</blockquote>
<p>
<h3>Notes</h3>
<p>If your decoder is threaded, it is recommended that you NOT call
<tt>ov_open_callbacks()</tt>
in the main control thread--instead, call <tt>ov_open_callbacks()</tt> IN your decode/playback
thread. This is important because <tt>ov_open_callbacks()</tt> may be a fairly time-consuming
call, given that the full structure of the file is determined at this point,
which may require reading large parts of the file under certain circumstances
(determining all the logical bitstreams in one physical bitstream, for
example).
See <a href="threads.html">Thread Safety</a> for other information on using libvorbisfile with threads.
<br><br>
<hr noshade>
<table border=0 width=100%>
<tr valign=top>
<td><p class=tiny>copyright &copy; 2003 Xiph.org</p></td>
<td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
</tr><tr>
<td><p class=tiny>Vorbisfile documentation</p></td>
<td align=right><p class=tiny>vorbisfile version 1.68 - 20030307</p></td>
</tr>
</table>
</body>
</html>